I'm pretty darn excited. I've been following Miguel de Icaza for a while (creator of mono, GNOME and some other stuff)
From what I gather Mono team will eventually help the newly open source .NET patch things up to run smoothly on Linux. They have said that now that the open source code of .NET is available they will improve Mono thus implementing all the things that were either broken, poorly implemented, etc.
I recently got a student license of Xamarin Studio (you can cross compile to iOS, Android, Mac, Linux etc) so I've been thinking of becoming an enthusiast (don't wanna go near the word evangelist yet).
All in all, great news. Really great news. And it's under the MIT License no less!